JP-2011-69316A (US 2011/0073056) describes a fluid-pressure-operated valve timing controller having an outer rotor rotating with a crankshaft and an inner rotor rotating with a camshaft inside of the outer rotor. The inner rotor defines operation chambers inside the outer rotor, and the operation chambers are arranged in a circumference direction. The inner rotor is slidably rotated in the circumference direction relative to the outer rotor by working fluid flowing into or out of the operation chambers, thus the valve timing can be controlled in accordance with relative rotation between the inner rotor and the outer rotor.
The valve timing controller has an element wire that spirally extends to form a spiral spring. The most outside circumference part of the wire is supported by the outer rotor, and the most inside circumference part of the wire is supported by the inner rotor. The spiral spring is twistingly deformed by rotation of the inner rotor in a deformation direction relative to the outer rotor, thereby biasing the inner rotor in a biasing direction opposite from the deformation direction relative to the outer rotor. Therefore, when the supply of working fluid is stopped to the operating chambers in a case where an engine is stopped, the spiral spring rotates the inner rotor in the biasing direction relative to the outer rotor. Thus, the valve timing that is suitable for the start-up of the engine can be compulsorily realized.
Generally, the engine has vibration by the rotation, and the frequency of vibrations is increased by increase in the rotation speed of the engine. If the frequency of vibrations is increased to be equal to a natural frequency of vibration of the spiral spring, resonance will occur in the spiral spring. As a result, stress applied to the spiral spring is rapidly increased, and the spiral spring may have a failure such as bending or crack.
Because the element wire extends spirally, a part of the wire is located adjacent with other part of the wire in the radial direction. The part of the wire and the other part of the wire are just in contact by only bringing the most outside circumference part inward in the radial direction, and are easily separated from each other when the spiral spring is twistingly deformed. In this case, the natural frequency of the spiral spring is reduced, and the resonance becomes easy to be generated in the spiral spring.
Moreover, while the most outside circumference part is brought inward at the contact position in the radial direction, the element wire may be tensioned outward in the radial direction at a position different from the contact position, and excessive stress is easily generated.
Furthermore, unnecessary force is applied in the radial direction to the most inside circumference part that is supported by the inner rotor, when the most outside circumference part is brought inward in the radial direction. At this time, a contact resistance generated between the inner rotor and the outer rotor is increased, and the responsivity of the valve timing may be lowered.